The present invention relates to a heat exchanger utilizing a tube bundle therein, and more particularly to a finned tube bundle oil cooler of the countercurrent type.
Tube bundle heat exchangers of the countercurrent type having an outer casing or shell receiving a tube bundle comprising a plurality of tubes secured between oppositely disposed headers adapted to be positioned in the ends of the casing are known in the heat exchange art. One fluid passes through the tubes from one end of the casing to the other, and a second fluid is introduced into the casing to flow in the opposite direction and in heat exchange relationship with the exterior surfaces of the tubes. Without more, this system provides a relatively inefficient system of heat exchange between the two fluids. To increase the heat exchange properties, a series of baffles are usually provided in the casing to alter the flow pattern of the fluid surrounding the tubes. The baffles generally take the form of discs closely conforming to the casing interior having openings formed therein through which the tubes pass and having portions removed from their peripheries to allow the passage of fluid from one side of the baffle to the other.
These baffles are generally termed segmental and are spaced apart from one another by tubular spacers which are positioned on longitudinally running "stay rods" during assembly. The baffles are arranged so that the cutaway portions alternately face opposite sides causing the fluid to alternate from one side of the casing to the other in a sinuous fashion to pass transversely across and around the tubes as it makes its way from one end of the casing to the other. Generally to minimize leakage, the baffles are brazed or soldered to the tubes of the bundle.
To further enhance the heat transfer characteristics, the tubes may also be supplied with fins to further increase the heat exchange surface area. These fins may be a plurality of radial flanges which are individually secured onto the exterior surface of each tube, or they may take the form of generally circular plates having openings receiving the tubes and cut-away portions on opposite sides to allow for the sinuous passage of the fluid around the plates and tubes and through the casing. In this arrangement, the stack of plates are aligned on the tubes with the cut-away portions aligned with the cut-away portions of the baffles; the baffles being spaced along the stack of plates with their cut-away portions alternating on opposite sides. Thus, fluid may pass parallel to the plates between a pair of adjacent baffles and transversely across the tubes and around the baffle plate through the cut-away portion to flow through the next set of plates in the opposite direction. The cut-away portions of the plates will act to distribute fluid longitudinally along the stack of plates. The stack of plates or fins acts to maximize the heat transfer surface between the two fluids.
The present invention is an improvement on the above described finned tube bundle with the elimination of the necessity for the series of baffle plates. To accomplish this, a plurality of circular metal plates are provided with openings to receive therethrough the tubes in the tube bundle; the circular plates having peripheries substantially conforming and sealingly received within the casing for the heat exchanger. Each plate is further provided with a plurality of slits therein to allow for generally axial flow of a liquid around the tubes through the casing in a direction countercurrent to the flow of liquid through the tubes. With the plates closely stacked on the tubes and conformably received in the casing, the flow of fluid is substantially axial along and around the tubes, but it is broken up into smaller streams and effectively turbulized by the plurality of slits in each plate.
Further, the slits in the fins serve as extended heat transfer surfaces for the fluid that is circulating around the tubes in the tube bundle, the slits in the fins increasing the heat transfer capacity through the interrupting of the fluid boundary layer on the surface of the fins. In addition to the heat transfer aspect of the fins, the slits formed in the fins act as baffles by directing the flow of fluid. In formation, the slitting of the fins by stamping forms a plurality of small louvres which, for each fin, are generally all oriented in one direction. When stacked together on the tube bundle, all of the fins may be positioned with the louvres oriented in one direction or alternate fins may be rotated to orient the louvres in opposite directions on adjacent fins.
Also, this fin stack may be utilized with a series of imperforate fins provided at intervals to act as baffles. Such baffles have openings for the tubes, but are otherwise imperforate and are cut-away at a portion of their peripheries to provide segmental plates oriented with the cut-away portions at alternate sides to provide a cross-flow action of the fluid relative to the tubes in a sinuous fashion.
An object of the present invention is the provision of a finned tube bundle heat exchanger having a plurality of slits formed in each fin between the tubes to improve the heat transfer characteristics of the heat exchanger.
Another object of the present invention is the provision of a finned tube bundle heat exchanger wherein the slits formed in the fins act as baffles for directing the flow of fluid generally axially along the tube bundle in the casing.
Further objects are to provide a construction of maximum simplicity, efficiency, economy and ease of assembly and operation, and such further objects, advantages and capabilities as will later more fully appear and are inherently possessed thereby.